When Koichi comes to visit his classmate Yosuke's house, he finds out that Yosuke's mother, Akari, is masturbating in the bath, and gets so excited that he starts masturbating right there. Akari notices this and gently scolds the embarrassed Koichi, then proposes a surprising relationship, saying, "Let's have fun together." Koichi refuses, fearing that it will damage his relationship with his best friend, but Akari, who is desperate to release her sexual frustration as her husband is constantly away on business, forcefully suggests that "If you only masturbate with the tip, it's the same as not doing anything," and he reluctantly accepts...